Hi there Sokunth Sirei,
It sounds like you are unable to see this audiobook you purchased for redownload. That is expected, since you cannot download audiobooks from the cloud again. According to the following article you may be able to find it on your computer in iTunes to sync over to your iPhone:
iBooks purchased on your iPhone, iPad, or iPod touch automatically download to your iBooks or iTunes library the next time you sync your device with your computer.
From: About iBooks
So as long as you had synced the device you made the purchase on you should be able to sync it back to your new iPhone using iTunes. You would sync that from your iTunes library the same way you would sync music, or photos. This article should help you do that:
Sync your iPhone, iPad, or iPod touch with iTunes using USB
Thank you for using Apple Support Communities, let us know how that goes!